1. Field of the Invention
The present disclosure relates to air conditioning systems. More particularly, the present disclosure relates to methods and systems for controlling air conditioning systems having a free-cooling mode and a cooling mode.
2. Description of Related Art
An air conditioning system operates by expending energy to cool a given volume of air. Typically, air conditioning systems are run in a chiller or cooling mode, which includes circulating a refrigerant through a thermodynamic cycle. During the cycle, heat and work are transferred to the refrigerant. The refrigerant enters a heat exchanger and chills a working fluid such as water, air, or glycol, which in turn can be used to cool a conditioned space. Work is generally transferred to the refrigerant using a compressor.
However, when the temperature of the ambient outside air is low, the outside air may be used to cool the refrigerant without engaging the compressor. When ambient outside air is used by an air conditioning system to cool the refrigerant, the system is referred to as operating in a free-cooling mode. Because running the air conditioning system in a free-cooling mode requires less work input, running the system in free-cooling mode is more efficient than running the system in cooling mode.
Traditionally, air conditioning systems have been run in cooling mode even when the ambient outside air temperature is low. Running in cooling mode under such conditions provides a low efficiency means of conditioning the refrigerant. In contrast, running the air conditioning system under such conditions in a free-cooling mode is more efficient. In the free-cooling mode, one or more ventilated heat exchangers and pumps are activated and the refrigerant circulating throughout the air conditioning system is cooled by outside ambient air without the need for a compressor.
Accordingly, there is a need for methods and systems for controlling the cooling capacity of air conditioning systems when those systems are operating in free-cooling mode.